1. Field of the Invention
The present invention relates to methods for removing coloring agents (carotenoids), from citrus fruits, and in particular relates to such methods which avoid the introduction of foreign substances, in order to maintain the natural purity of the resulting product.
2. Description of the Prior Art
Citrus fruits, such as oranges, include an outer, colored skin (referred to as the "flavedo") and an inner, white skin (the "albedo"). The flavedo is made up of a multitude of tiny cells, each containing a complex liquid generally referred to as "peel oil." This peel oil includes, among many others, compounds which establish the color and flavor of the peel and the fruit. The coloring agents in the peel, which are referred to generically as carotenoids, are themselves a complex mixture of organic compounds.
The carotenoids of orange peels potentially have many important commerical uses. For example, juices prepared from fruit in the early part of the growing season often have poor coloring. It is possible to add carotenoids extracted from the peel to "bolster" the color of early season products. Further, such coloring agents have many commerical uses in the coloring of other food products. However, agricultural regulations prohibit the addition of foreign substances, such as organic solvents, to citrus juices and other edibles. As is described further below, the prior art teaches the use of such organic solvents as a means for deriving carotenoids from the flavedo.
These prior art teachings suggest numerous techniques for extracting the carotenoid coloring agents found in the flavedo. In the Proceedings of the Florida State Horticultural Society, volume 81, pages 264-268 (1968), Ting and Henrickson disclose a process in which the flavedo was finely chopped and the oil therein dissolved in an aqueous acetone solution.
In Food Technology, volume 23, (7), pages 87-90 (1969), Ting and Hendrickson describe their earlier work and disclose the use of an admixture of acetone and hexane as a solvent used to dissolve the oils in the flavedo. The resulting solution was then distilled to remove hexane, limonene and other low boiling point constituents. The authors further describe a technique for purifying the extracted carotenoids chromatographically in conjunction with a Florasil Column.
In the Journal of Food Science, volume 35, pages 436-439 (1970), Kew and Berry teach the use of hexane alone as a solvent to dissolve the oils in chopped flavedo, followed by a treatment of the resulting solution with potassium hydroxide; the solution was then washed with water and evaporated. The coloring agents were then steam distilled from the remaining constituents.
In the Journal of Food Science, volume 36, pages 1033-1035 (1971), Wilson, Bissett and Berry also made disclosure to a counter-current extraction to further purify the carotenoids derived from peel frits, whole peel and flavedo. The authors described the flavedo input as providing the best yield of color.
A slightly different approach to the problem of carotenoid purification after extraction is taught by Berry, Wilson and Bissett in the Journal of Food Science, volume 37, pages 809-811 (1972). In this article, the authors disclosed the use of isopropyl alcohol, following the steam distillation step. Because the carotenoids are soluble in the alcohol and the undesirable constituents are not, these other ingredients were removed by filtering. The carotenoids were then precipitated from the alcohol.
At volume 36 of the Journal of Food Science, pages 367-369 (1971), the authors describe a study to determine the stability of the carotenoids during extended periods of storage.
Judah, Burdick, and Carroll, in Industrial and Engineering Chemistry, Volume 46 (no. 11), pages 2262-2271 (November 1954). disclose the use of alcohols in a manner similar to that described by Berry, Wilson and Bissett (Journal of Food Science, volume 37) as a means for extracting chlorophyl from dried leaf meal.
While the above described techniques provide relatively efficient methods for extracting concentrated amounts of the citrus carotenoids, the resulting product includes amounts of the foreign solvents therein and therefore prevent the use of carotenoids obtained by these methods as additives to certain food products.
There have also been suggestions for using compounds naturally occuring in citrus peel as a solvent for removing the carotenoids from the flavedo. However, these compounds proved unsatisfactory, requiring the use of acetone or similar solvents as a polishing step for final removal of the carotenoids.
In U.S. Pat. No. 3,915,960, which is assigned to the assignee of the present invention, Waite and Jefferson disclose a method for the accelerated winterization of citrus oils.